1. Field of the Invention
The present invention relates to a technology for encoding a moving picture using a motion vector. More particularly, this invention relates to a technology for performing high-precision error correction using a motion vector without performing a motion search.
2. Description of the Related Art
In picture transmission systems, if a transmission error occurs, a decoding process is not successfully performed in a decoder, and at worst, the decoder may hang. According to Moving Picture Experts Group (MPEG), if a decoding error once occurs, the decoding process cannot be performed until it reaches a next recovery point, and occurrence of an error becomes a significant cause of picture degradation.
Following two measures have been taken so far against the decoding error:                (1) Assume that an MPEG decoder includes a motion search circuit. In this case, when detecting a decoding error, the MPEG decoder recognizes an error position, and temporally handles a reference picture in a previous frame from the frame in which an error has occurred, as a corrected picture for the error position, as it is.        (2) Assume that an MPEG decoder includes a motion search circuit. In this case, when detecting a decoding error, the MPEG decoder recognizes an error position, and executes a motion search to an adjacent macroblock (MB) related to the error position. Then, the MPEG decoder acquires a corrected picture from a reference picture using the result of motion search.        
A conventional MPEG decoder has been disclosed in, for example, Japanese Patent Application Laid-Open No. 2001-309388.
In the case of (1), however, since the reference picture in the temporally previous frame is used as the corrected picture for the error position, the picture in the previous frame is followed by the same picture. Therefore, it seems as if the video is motionless.
In the case of (2), to incorporate the motion search circuit, the size of the MPEG decoder becomes large. In addition, because the MPEG decoder executes the motion search in, amount of processing increases, which lengthens the processing time.